Three dimensional displays generally suffer from a problem of inducing eye strain in some viewers due to conflicts between accurate presentation of stereopsis, vergence and accommodation. For example, 3D displays generally require a viewer to always focus at the screen plane to keep it in focus, but depth cues from accommodation are inconsistent with depth cues from vergence.
For example, as the focal plane remains at the plane of the screen, a viewer's eyes are forced to converge on stereoscopic objects whose parallax implies a position in space which differs from the screen plane. Consider a screen plane 10 feet away from a viewer. Their eyes remain focused on the screen plane, however a stereoscopic presentation implies that an object is 15 feet away from the viewer. The object then moves from an implied 15 feet away from the viewer to an implied 7 feet away from the viewer. All the while the eyes remain accommodated/focused on a fixed screen plane that is 10 feet away.
The human brain has short-cuts in it that allow humans to expect a learned response, or muscle memory level of accommodation/focus. The systems of vergence and focus are thus normally cooperative. In a stereo solution with a planar display the viewer is asked to decouple this relationship that the viewer has learned to utilize to gauge distance. This decoupling induces fatigue and stress over time.